Semi-active partial parallel battery architecture for an automotive vehicle systems and methods

ABSTRACT

An automotive battery system that includes a lead-acid battery electrically coupled to a first bus, in which the lead-acid battery supplies electrical power to a starter via the first bus to cold crank an internal combustion engine of a vehicle; a lithium-ion battery electrically coupled to a second bus, in which the lithium-ion battery captures and stores electrical energy generated by a regenerative braking system when the vehicle brakes and supplies electrical power to the second bus using the electrical energy captured from the regenerative braking system such that a first portion of the second electrical power is supplied to an electrical system; and a DC/DC converter electrically coupled between the first bus and the second bus, in which the DC/DC converter controls supply of a second portion of the second electrical power to charge the lead-acid battery.

CROSS REFERENCE TO RELATED APPLICATIONS

Under 35 U.S.C. § 120, this application is a continuation of U.S. patentapplication Ser. No. 14/938,664 filed Nov. 11, 2015, which claimspriority from and benefit of U.S. Provisional Application Ser. No.62/079,848 filed Nov. 14, 2014, both of which are incorporated byreference herein in their entireties for all purposes.

BACKGROUND

The present disclosure relates generally to the field of battery systemsand, more particularly, to battery systems that may be used in anautomotive vehicle context.

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present disclosure,which are described below. This discussion is believed to be helpful inproviding the reader with background information to facilitate a betterunderstanding of the various aspects of the present disclosure.Accordingly, it should be understood that these statements are to beread in this light, and not as admissions of prior art.

A vehicle that uses one or more battery systems for providing all or aportion of the motive power for the vehicle can be referred to as anxEV, where the term “xEV” is defined herein to include all of thefollowing vehicles, or any variations or combinations thereof, that useelectric power for all or a portion of their vehicular motive force. Forexample, xEVs include electric vehicles (EVs) that utilize electricpower for all motive force. As will be appreciated by those skilled inthe art, hybrid electric vehicles (HEVs), also considered xEVs, combinean internal combustion engine propulsion system and a battery-poweredelectric propulsion system, such as 48 Volt (V) or 130V systems.

The term HEV may include any variation of a hybrid electric vehicle. Forexample, full hybrid systems (FHEVs) may provide motive and otherelectrical power to the vehicle using one or more electric motors, usingonly an internal combustion engine, or using both. In contrast, mildhybrid systems (MHEVs) disable the internal combustion engine when thevehicle is idling and utilize a battery system to continue powering theair conditioning unit, radio, or other electronics, as well as torestart the engine when propulsion is desired. The mild hybrid systemmay also apply some level of power assist, during acceleration forexample, to supplement the internal combustion engine. Mild hybrids aretypically 96V to 130V and recover braking energy through a belt or crankintegrated starter generator.

Further, a micro-hybrid electric vehicle (mHEV) also uses a “Stop-Start”system similar to the mild hybrids, but the micro-hybrid systems of amHEV may or may not supply power assist to the internal combustionengine and operates at a voltage below 60V. For the purposes of thepresent discussion, it should be noted that mHEVs typically do nottechnically use electric power provided directly to the crankshaft ortransmission for any portion of the motive force of the vehicle, but anmHEV may still be considered as an xEV since it does use electric powerto supplement a vehicle's power needs when the vehicle is idling withinternal combustion engine disabled and recovers braking energy throughan integrated starter generator. In addition, a plug-in electric vehicle(PEV) is any vehicle that can be charged from an external source ofelectricity, such as wall sockets, and the energy stored in therechargeable battery packs drives or contributes to drive the wheels.PEVs are a subcategory of EVs that include all-electric or batteryelectric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), andelectric vehicle conversions of hybrid electric vehicles andconventional internal combustion engine vehicles.

xEVs as described above may provide a number of advantages as comparedto more traditional gas-powered vehicles using only internal combustionengines and traditional electrical systems, which are typically 12Vsystems powered by a lead acid battery. For example, xEVs may producefewer undesirable emission products and may exhibit greater fuelefficiency as compared to traditional internal combustion vehicles and,in some cases, such xEVs may eliminate the use of gasoline entirely, asis the case of certain types of EVs or PEVs. Further, dual battery xEVtechnology has led to reductions in undesirable emissions compared tomore traditional gas-powered vehicles. For example, regenerative brakingvehicles capture and store electrical energy generated when the vehicleis braking or coasting. The captured electrical energy may then beutilized to supply power to the vehicle's electrical system. As anotherexample, battery modules in accordance with present embodiments may beincorporated with or provide power to stationary power systems (e.g.,non-automotive systems).

As technology continues to evolve, there is a need to provide improvedpower sources, particularly battery modules, for such vehicles. Based onthe advantages over traditional gas-power vehicles, manufactures maydesire to utilize improved vehicle technologies (e.g., regenerativebraking systems) within their vehicle lines. To implement the improvedvehicle technologies, the manufacturer may find it desirable to adjustconfiguration of their traditional vehicle platforms. For example, it isnow recognized that, to improve advantages provided by a regenerativebraking system, a manufacturer may wish to adjust configuration of abattery system to improve efficiency with which the battery systemsupplies and/or captures electrical energy generated during regenerativebraking.

SUMMARY

Certain embodiments commensurate in scope with the disclosed subjectmatter are summarized below. These embodiments are not intended to limitthe scope of the disclosure, but rather these embodiments are intendedonly to provide a brief summary of certain disclosed embodiments.Indeed, the present disclosure may encompass a variety of forms that maybe similar to or different from the embodiments set forth below.

A first embodiment describes an automotive battery system that includesa lead-acid battery electrically coupled to a first bus, in which thelead-acid battery supplies electrical power to a starter via the firstbus to cold crank an internal combustion engine of a vehicle; alithium-ion battery electrically coupled to a second bus, in which thelithium-ion battery captures and stores electrical energy generated by aregenerative braking system when the vehicle brakes and supplieselectrical power to the second bus using the electrical energy capturedfrom the regenerative braking system such that a first portion of thesecond electrical power is supplied to an electrical system; and a DC/DCconverter electrically coupled between the first bus and the second bus,in which the DC/DC converter controls supply of a second portion of thesecond electrical power to charge the lead-acid battery.

A second embodiment describe a method for operating a battery systemincluding cold cranking, using a starter, an internal combustion enginewhen a vehicle is transitioned from key off to key on, in which a firstbattery of the battery system supplies first electrical power to thestarter to cold crank the internal combustion engine; converting, usinga regenerative braking system, mechanical energy from motion of thevehicle into electrical energy; capturing, using a second battery of thebattery system, the electrical energy generated by the regenerativebraking system; outputting a second electrical power from the secondbattery using the electrical energy generated by the regenerativebraking system; and controlling, using a DC/DC converter, supply of afirst portion of the second electrical power to an electrical system ofthe vehicle and supply of a second portion of the second electricalpower to the first battery.

A third embodiment describes a tangible, non-transitory,computer-readable medium that stores instructions executable by aprocessor in a vehicle. The instructions include instruction toinstruct, using the processor, a battery system of the vehicle todisconnect a first battery from a starter of the vehicle to enable asecond battery to supply first electrical power to the starter by itselfto cold crank an internal combustion engine when the vehicle transitionsfrom key off to key on; determine, using the processor, whether state ofcharge of the first battery is greater than a first threshold; instruct,using the processor, an alternator of the vehicle to convert firstmechanical energy from the internal combustion engine into firstelectrical energy when the state of charge of the first battery is notgreater than the first threshold such that at least a portion of secondelectrical power output by the alternator is used to charge the firstbattery above the first threshold; and instruct, using the processor,the battery system to control division of third electrical power outputfrom the first battery between a first portion used to charge the secondbattery and a second portion used to power an electrical system of thevehicle when the state of charge of the first battery is greater thanthe first threshold.

DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is perspective view of a vehicle (an xEV) having a battery systemcontributing all or a portion of the power for the vehicle, inaccordance with an embodiment of the present approach;

FIG. 2 is a cutaway schematic view of the xEV of FIG. 1 in the form of ahybrid electric vehicle (HEV), in accordance with an embodiment of thepresent approach;

FIG. 3 is a schematic view of the battery system of FIG. 1, inaccordance with an embodiment;

FIG. 4 is a graph illustrating voltage characteristics o various batterychemistries, in accordance with an embodiment;

FIG. 5 is a graph illustrating voltage characteristics of non-voltagematched battery chemistries, in accordance with an embodiment;

FIG. 6 is a graph illustrating voltage characteristics of partialvoltage matched battery chemistries, in accordance with an embodiment;

FIG. 7 is a graph illustrating voltage characteristics of voltagematched battery chemistries, in accordance with an embodiment;

FIG. 8 is a schematic diagram of the battery system of FIG. 1 in aswitch-passive parallel battery architecture, in accordance with anembodiment;

FIG. 9 is a schematic diagram of the battery system of FIG. 1 in asemi-active partial parallel battery architecture, in accordance with anembodiment;

FIG. 10 is a flow diagram of a process for supplying electrical powerfrom the battery system of FIG. 1 when transitioned to key on, inaccordance with an embodiment;

FIG. 11 is a flow diagram of a process for supplying electrical powerfrom the battery system of FIG. 1 to warm crank an internal combustionengine, in accordance with an embodiment; and

FIG. 12 is a flow diagram of a process for supplying electrical powerfrom the battery system of FIG. 1 when transited to key off, inaccordance with an embodiment.

DETAILED DESCRIPTION

One or more specific embodiments of the present techniques will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

As discussed above, vehicle technology has improved to increase fueleconomy and/or reduce undesirable emissions compared to traditionalgas-powered vehicles. For example, a vehicle may include a regenerativebraking system to convert mechanical energy of the vehicle intoelectrical energy while the vehicle brakes. A battery system may capturethe electrical energy for subsequent supply to electrical components ofthe vehicle, such as the air conditioner and/or the radio.

In traditional gas-power vehicles, an internal combustion engine maydrive an alternator to generate electrical energy used to powerelectrical components of the vehicle. The regenerative braking systemmay enable the alternator to be disabled for longer periods of time,thereby reducing load on the internal combustion engine. As such, theinternal combustion engine may burn less fuel and, thus, reduceundesired emissions and/or increase fuel economy of the vehicle.

Based on the advantages over traditional gas-power vehicles,manufactures may desire to utilize improved vehicle technologies (e.g.,regenerative braking technology) within their vehicle lines. Thesemanufactures often utilize one of their traditional vehicle platforms asa starting point. Generally, traditional gas-powered vehicles aredesigned to utilize battery systems that include a single twelve voltlead-acid (PbA) battery. It may be possible to utilize traditionalbattery systems with improved vehicle technologies, such as aregenerative braking system. For example, a lead-acid battery maycapture and store electrical energy generated during regenerativebraking for subsequent supply to electrical components of the vehicle.

However, using the lead-acid battery to capture electrical energygenerated during regenerative braking may limit operational efficiencyof the battery system. More specifically, compared to other batterychemistries, a lead-acid battery may have a lower coulombic efficiencyand/or a lower charge acceptance rate limit. As used herein, “coulombicefficiency” and “charge acceptance rate limit” may be usedinterchangeably to describe efficiency with which a battery captures andstores electrical energy. In other words, a lead-acid battery may becapable of capturing and storing less electrical energy at one timecompared to, for example, a lithium-ion (Li-ion) battery. As such, usinga single lead-acid battery may limit an amount of electrical energycaptured during regenerative braking and, thus, limit advantagesprovided by the regenerative braking system.

Accordingly, as will be described in more detail below, embodiments ofthe present disclosure provide techniques to improve operationalefficiency of a battery system by including multiple batteries withdiffering battery configurations. As used herein, “battery” is intendeddescribe an energy storage device that utilize a chemical reaction tostore and/or distribute electrical power. Additionally, as used herein“battery configuration” is intended to describe properties of thebattery, such as output voltage and/or battery chemistry. Thus, in someembodiments, the battery system may include a first battery that iselectrically connected to twelve voltage electrical components and asecond battery that is electrically connected to forty-eight voltageelectrical components. Additionally, in some embodiments, the batterysystem may include a first battery with a lead-acid battery chemistryand a second battery with a lithium-ion battery chemistry.

Utilizing multiple batteries with differing battery chemistries mayfacilitate utilizing strengths of the different battery chemistries. Forexample, since less affected by cold temperatures and deep discharging,the battery system may use the lead-acid battery to cold crank theinternal combustion engine. As used herein, “cold crank” is intended todescribe starting the internal combustion engine when transitioning fromkey off to key on. Additionally, since having a higher coulombicefficiency and/or a higher charge acceptance rate limit, the batterysystem may use the lithium-ion battery to capture and store electricalenergy generated during regenerative braking. In other words, thebattery system may divide operations between the multiple batteriesbased at least in part on their respective strengths.

Various architectures (e.g., configurations) may be used for a batterysystem. However, some may be better suited for dividing operationsbetween multiple batteries, for example, by simplifying control schemeand/or increasing amount of control over operation of the batterysystem. One architecture may be semi-active partial parallel batteryarchitecture. In this architecture, a first battery (e.g., a lead-acidbattery) may be electrically connected in parallel with a starter usedto crank the internal combustion engine via a first bus. Additionally, asecond battery (e.g., a lithium-ion battery) may be connected inparallel with an electrical system (e.g., electrical components of thevehicle) and a regenerative braking system via a second bus.Additionally, a DC/DC converter may be electrically coupled between thefirst bus and the second bus.

In this manner, the battery system may use the DC/DC converter tocontrol electrical power flowing between the first bus and the secondbus. For example, the DC/DC converter may disconnect the first bus andthe second bus during a cold cranking to enable the first battery tosupply electrical power to the starter by itself. Additionally, theDC/DC converter may disconnect the first bus and the second bus duringregenerative braking to enable the second battery to capture thegenerated electrical energy by itself. Furthermore, the DC/DC convertermay control magnitude of current flowing from the second bus to thefirst bus to control charging rate of the first battery, for example,based on its charge acceptance rate limit and/or power consumption bythe electrical system.

As such, the semi-active partial parallel architecture may facilitatedividing operations between the first battery and the second battery,for example, based on their respective strengths, to improve operationalefficiency of the battery system. In fact, in some embodiments, thebattery system may use a battery to only perform operations it is bestsuited for. For example, the battery system may use a first battery(e.g., lead-acid battery) only to crank the internal combustion engine,but not to capture electrical energy generated during regenerativebraking or to supply electrical power to the electrical system. In suchan embodiment, storage capacity and, thus, physical size of the firstbattery may be reduced, which may facilitate reducing overall size ofthe battery system. Additionally, the battery system may use the secondbattery (e.g., lithium-ion battery) to gradually charge the firstbattery while also supplying electrical power to the electrical system.In such embodiments, current capacity of the DC/DC converter may bereduced, which may facilitate reducing overall size and/or cost of thebattery system.

To help illustrate, FIG. 1 is a perspective view of an embodiment of avehicle 10, which may utilize a regenerative braking system. Althoughthe following discussion is presented in relation to vehicles withregenerative braking systems, the techniques described herein areadaptable to other vehicles that capture/store electrical energy with abattery, which may include electric-powered and gas-powered vehicles.

It is now recognized that it is desirable for a non-traditional batterysystem 12 (e.g., a lithium ion car battery) to be largely compatiblewith traditional vehicle designs. In this respect, present embodimentsinclude various types of battery modules for xEVs and systems thatinclude xEVs. Accordingly, the battery system 12 may be placed in alocation in the vehicle 10 that would have housed a traditional batterysystem. For example, as illustrated, the vehicle 10 may include thebattery system 12 positioned similarly to a lead-acid battery of atypical combustion-engine vehicle (e.g., under the hood of the vehicle10). Furthermore, as will be described in more detail below, the batterysystem 12 may be positioned to facilitate managing temperature of thebattery system 12. For example, in some embodiments, positioning abattery system 12 under the hood of the vehicle 10 may enable an airduct to channel airflow over the battery system 12 and cool the batterysystem 12.

To simplify discussion, the battery system 12 will be discussed as beingdisposed under the hood of the vehicle 10, as depicted in FIG. 2. Asdescribed above, the battery system 12 may be electrically connected toelectrical components in the vehicle 10. For illustrative purposes, theelectrical components in the depicted embodiment include a starter 16, aregenerative braking system 20, a vehicle console 22, and a heating,ventilation, and air conditioning (HVAC) system 24.

In this manner, the battery system 12 may supply electrical power to oneor more electrical components in the vehicle 10 via one or more busses25. For example, the battery system 12 may supply electrical power tothe starter 16 to crank (e.g., start) an internal combustion engine 18.In some embodiments, the starter 16 may use the electrical power togenerate a spark that starts combustion in the internal combustionengine 18.

Additionally, the battery system 12 supply electrical power to otherelectrical components, such as the vehicle console 22 and the HVACsystem 24. As used herein, the other electrical components arecollectively referred to as the “electrical system.” Thus, theelectrical system may include a radiator cooling fan, a climate controlsystem, an electric power steering system, an active suspension system,an auto park system, an electric oil pump, an electricsupercharger/turbocharger, an electric water pump, a heatedwindscreen/defroster, a window lift motor, a vanity light, a tirepressure monitoring system, a sunroof motor control, a power seat, analarm system, an infotainment system, a navigation feature, a lanedeparture warning system, an electric parking brake, an external light,or any combination thereof.

Additionally, the battery system 12 may receive electrical power fromone or more electrical components in the vehicle 10. For example, thebattery system 12 may receive electrical power output from theregenerative braking system 20 when the vehicle 10 is braking. Asdescribed above, the regenerative braking system 20 may outputelectrical power by converting mechanical energy of the vehicle 10 intoelectrical energy. More specifically, the vehicle 10 may have mechanical(e.g., kinetic) energy due to its motion. When braking, the vehiclereduces its motion and, thus, its mechanical energy. This reduction inmechanical energy may be dissipated as heat, for example, produced bytraditional brake pads.

Additionally or alternatively, the regenerative braking system 20 mayconvert at least a portion of this reduction in mechanical energy intoelectrical energy using a generator, such as the alternator, a beltstarter generator (BSG), an electric motor, or the like. In someembodiments, the motion of the vehicle 10 may be used to actuate thegenerator, thereby consuming mechanical energy of the vehicle 10 andgenerating electrical energy. For example, the regenerative brakingsystem 20 may mechanically connect the alternator to the wheels of thevehicle 10 so that rotation of the wheels may actuate the alternator,thereby reducing speed of the vehicle and outputting electrical power.

As described above, the battery system 12 may utilize multiple batterieswith varying battery configurations to improve operational efficiency.To help illustrate, a more detailed view of an embodiment of the batterysystem 12 and a control unit 32 used to control operation of the batterysystem 12 are described in FIG. 3. In the depicted embodiment, thebattery system 12 includes a first battery 26, a second battery 28, oneor more sensors 29, and one or more controllable switching devices 30.Although described with regard to two batteries, other embodiments mayinclude two or more batteries with varying battery configurations (e.g.,output voltage and/or battery chemistry). For example, in otherembodiments, the battery system 12 may include three batteries each witha different battery chemistry and/or a different output voltage.

As described above, the battery system 12 may be electrically connectedto various electrical components in the vehicle 10. Generally,electrical components are designed to operate with specific electricalpower (e.g., specific voltage). Thus, in some embodiments, electricalcomponents in the vehicle 10 may be desired to operate with differentvoltages. For example, a first component may be designed or configuredto operate with twelve volt electrical power while a second componentmay be designed or configured to operate with forty-eight voltelectrical power.

Thus, utilizing multiple batteries with varying battery configurationsmay facilitate electrically connecting the battery system 12 withelectrical components designed to operate at different voltages.Generally, electrical power output by a battery may depend at least inpart on configuration of its battery cells 34. For example, connectingbattery cells 34 in series may enable increasing voltage of the batteryand connecting battery cells 34 in parallel may enable increase currentof the battery. Thus, continuing with the above example, battery cells34 of the first battery 26 may be configured so that the first battery26 is a twelve voltage battery and battery cells 34 of the secondbattery 28 may be configured so that the second battery is a forty-eightvolt battery. As such, the battery system 12 may use the first battery26 to electrically connect with the first component and the secondbattery 28 to electrically connect with the second component.

Additionally, the battery system 12 may include multiple batteries withvarying battery chemistries to utilize the strengths of the differentbattery chemistries. Generally, different battery chemistries may havedifferent operational characteristics, such as open-circuit voltage,charge acceptance rate limit, coulombic efficiency, designed operatingtemperature range, and the like.

To help illustrate, characteristics of multiple twelve volt batterieswith different battery chemistries are described with respect to FIG. 4.Specifically, the batteries include a lithium nickel manganese cobaltoxide (NMC) battery, a lithium-titanate/lithium nickel manganese cobaltoxide (NMC/LTO) battery, a lithium-titanate/lithium manganese oxide(LMO/LTO) battery, a nickel-metal hydride (NiMH) battery, a nickel-zinc(NiZn) battery, a lithium iron phosphate (LFP) battery, and a lead-acid(PbA) battery are described. In some embodiments, an NMC battery cellmay include a lithium nickel manganese cobalt oxide cathode with agraphite anode, a NMC/LTO battery cell may include a lithium manganeseoxide cathode with a lithium-titanate anode, an LMO/LTO battery cell mayinclude a lithium manganese oxide cathode and a lithium-titanate anode,and an LFP battery cell may include a lithium iron phosphate cathode anda graphite anode.

As depicted, FIG. 4 is an XY plot that describes the voltagecharacteristics of each of the batteries over its total state of charge(e.g., from 0% state of charge to 100% state of charge), in which stateof charge is shown on the X-axis and voltage is shown on the Y-axis. Assuch, the depicted embodiment includes an NMC voltage curve 38 thatdescribes voltage characteristics of the NMC battery, a NMC/LTO voltagecurve 40 that describes voltage characteristics of the NMC/LTO battery,a NiMH voltage curve 42 that describes voltage characteristics of theNiMH battery, a LFP voltage curve 44 that describes voltagecharacteristics of the LFP battery, a LMO/LTO voltage curve 46 thatdescribes voltage characteristics of the LMO/LTO battery, a NiZn voltagecurve 48 that describes voltage characteristics of the NiZn battery, anda PbA voltage curve 50 that describes voltage characteristics of thelead-acid battery.

As depicted, the batteries may each have different open circuit voltageranges. Thus, different pairs of battery chemistries selected for thefirst battery 26 and the second battery 28 may cause the battery system12 to operate differently. In some embodiments, operation of the batterysystem 12 may be based at least in part on an amount the open circuitvoltage ranges of the first battery 26 and the second battery 28overlap. For example, the chemistry pair selected may cause the firstbattery 26 and the second battery 28 to be non-voltage matched, partialvoltage matched, or voltage matched. As used herein, “non-voltagematched” is intended to describe when the first battery 26 and thesecond battery 28 open circuit voltage ranges do not overlap, “partialvoltage matched” is intended to describe when the first battery 26 andthe second battery 28 open circuit voltage ranges partially overlap(e.g., between 1-74% of the total state of charge of the second battery28), and “voltage matched” is intended to describe when the firstbattery 26 and the second battery 28 voltages largely overlap (e.g.,between 75-100% of the total state of charge of the second battery 28).

To help illustrate, voltage curves for a pair of non-voltage matchedbatteries are depicted in FIG. 5, voltage curves for a pair of partialvoltage matched batteries are depicted in FIG. 6, and voltage curves fora pair of voltage matched batteries are depicted in FIG. 7. Forillustrative purposes, in FIGS. 5-7, the first battery 26 will bedescribed as a lead-acid battery and the second battery 28 will bedescribed as different lithium-ion batteries (e.g., a NMC battery, aNMC/LTO battery, and a LMO/LTO battery).

As depicted in FIGS. 4-7, the voltage of each battery may vary with itsstate of charge (SOC). For example, a lead-acid battery may have anopen-circuit voltage of 11.2 volts at 0% state of charge, 12.2 volts at50% state of charge, and 12.9 volts at 100% state of charge. As such,the lead-acid battery may have an open-circuit voltage range between11.2-12.9 volts. Although the following discussion is made in referenceto a lead-acid battery and a lithium battery, the present techniques maybe applied to other battery pairings that have the similarcharacteristics (e.g., non-voltage matched, partial voltage matched, ornon-voltage matched).

As depicted in FIG. 5, when the second battery 28 is a NMC battery, thefirst battery 26 and the second battery 28 are non-voltage matchedbecause at no point do the PbA voltage curve 50 and the NMC voltagecurve 38 overlap. In other words, regardless of their respective stateof charge (SOC), the open circuit voltage of the first battery 26 andthe second battery 28 voltages do not overlap. To help illustrate, thefirst battery 26 has an open circuit voltage range of 11.2-12.9 voltsand the second battery 28 has an open circuit voltage range between13.3-16.4 volts. Accordingly, when the second battery 28 is at itslowest voltage (e.g., at 0% state of charge), its voltage isapproximately 13.3 volts. On the other hand, when the first battery 26is at its highest voltage (e.g., 100% state of charge), its voltage isapproximately 12.9 volts. In other embodiments, the first battery 26 andthe second battery 28 may also be non-voltage matched when the firstbattery 26 is a lead-acid battery and the second battery 28 is a LithiumNickel Cobalt Aluminum Oxide (NCA) (e.g., NCA cathode with graphiteanode), or a NMC-NCA battery (e.g., blended NMC-NCA cathode withgraphite anode).

As depicted in FIG. 6, when the second battery 28 is a NMC/LTO battery,the first battery 26 and the second battery 28 are partial voltagematched because the PbA voltage curve 50 and the NMC/LTO voltage curve40 partially overlap. As described above, the first battery 26 and thesecond battery 28 may be partial voltage matched when the voltageoverlap corresponds to between 1-74% of total state of charge range ofthe second battery 28. In other words, depending on their respectivestates of charge, the open circuit voltage of the first battery 26 andthe second battery 28 may be the same.

To help illustrate, the first battery 26 has an open circuit voltagerange between 11.2-12.9 volts and the second battery 28 has an opencircuit voltage range between 11.8-16 volts. Thus, open-circuit voltagesmay overlap when the first battery 26 and the second battery 28 are bothbetween 11.8-12.9 volts. As depicted, the second battery 28 has an opencircuit voltage of approximately 11.8 volts when at 0% state of chargeand 12.9 volts when at 20% state of charge. Thus, the open-circuitvoltages may overlap when the second battery 28 is between 0-20% stateof charge (e.g., 20% of total state of charge range of the secondbattery 28). In other embodiments, the first battery 26 and the secondbattery 28 may also be partial voltage matched when the first battery 26is a lead-acid battery and the second battery 28 is a NiMH, a LFPbattery, or a NMC/LTO-LMO battery (e.g., NMC-LMO cathode with LTOanode).

As depicted in FIG. 7, when the second battery 28 is a LMO/LTO battery,the first battery 26 and the second battery 28 are voltage matchedbecause the PbA voltage curve 50 and the LMO/LTO voltage curve 46largely overlap. As described above, the first battery 26 and the secondbattery 28 may be voltage matched when the voltage overlap correspondsto between 75-100% of the second battery's total state of charge range.In other words, the open circuit voltage of the first battery 26 and theopen circuit voltage of the second battery 28 may be the same for mostof their respective states of charge.

To help illustrate, the first battery 26 has an open circuit voltagerange of 11.2-12.9 volts and the second battery 28 has an open circuitvoltage range between 11.5-13.3 volts. Thus, open-circuit voltage mayoverlap when the first battery and the second battery are both between11.5-12.9 volts. As depicted, the second battery 28 has an open circuitvoltage of approximately 11.5 at 0% state of charge and 12.9 at 75%state of charge. Thus, open-circuit voltage may overlap when the secondbattery is between 75-100% state of charge (e.g., 75% of total state ofcharge of the second battery 28). In other embodiments, the firstbattery 26 and the second battery 28 may also be voltage matched whenthe first battery 26 is a lead-acid battery and the second battery 28 isa NiZn battery.

In addition to voltage ranges, other operational characteristics may beaffected by battery chemistry, such as charge acceptance rate limit,coulombic efficiency, designed operating temperature range, and thelike. For example, lead-acid batteries may be less affected by deepdischarging and be designed to have a larger operating temperature rangecompared to lithium-ion batteries. On the other hand, lithium ionbatteries may have a higher coulombic efficiency and/or a higher chargepower acceptance compared to lead-acid batteries.

As such, the battery chemistries used in first battery 26 and the secondbattery 28 may selected to utilize advantages of multiple differentbattery chemistries. For example, the first battery 26 may utilize alead-acid battery chemistry and the second battery 28 may utilize alithium-ion battery chemistry. To facilitate utilizing advantages,operations performed by the battery system 12 may be divided between thefirst battery 26 and the second battery 28 based on their respectivestrengths. For example, the first battery 26 may be utilized to coldcrank the internal combustion engine 18 due to its ability to operate atlower temperatures and being less affected by deep discharging.Additionally, the second battery 28 may be utilized to capture and storeelectrical energy generated during regenerative braking due to itshigher coulombic efficiency and/or higher charge power acceptance.

In embodiments such as depicted in FIG. 3, the control unit 32 maycontrol operation of the battery system 12 and/or other components ofthe vehicle 10, such as the regenerative braking system 20, analternator, the starter 16, the HVAC system 24, and/or the vehicleconsole 22. In other words, as used herein, the control unit 32 isintended to describe control components of the vehicle 10, which mayinclude a battery control unit, a vehicle control unit, and the like.

In some embodiment, the control unit 32 may control operation of thebattery system by instructing a controllable switching device 30 to openor close. In this manner, the battery system 12 may selectively connectand disconnect the first battery 26 and/or the second battery 28 fromelectrical components in the vehicle 10. Thus, in some embodiments, thecontrollable switching devices 30 may include one or more mechanicalswitches 52 and/or one or more direct current-to-direct current (DC/DC)converters 54, such as one or more boost converters, one or more buckconverters, and/or one or more bi-directional converters (e.g.,boost-buck converters).

Additionally, in some embodiments, the control unit 32 may controloperation based at least in part on operational parameters of thebattery system 12, such as temperature, state of charge, output voltage,bus voltage, output current, bus current, and the like. To facilitatedetermining the operational parameters, the control unit 32 may receivemeasurements from one or more sensors 29 in the battery system 12. Insome embodiments, the sensors 29 may directly measure the operationalparameters. Thus, in such embodiments, the sensors 29 may include one ormore temperature sensors to measure state of charge, one or moretemperature sensors to measure temperature, and/or one or more powersensors to measure electrical power of the first battery 26, the secondbattery 28, and/or a bus 25. Additionally or alternatively, the controlunit 32 may determine the operational parameters based at least in parton the measurements from the sensors 29.

To facilitate controlling operation, the control unit 32 may includememory 56 and one or more processors 58. Specifically, a processor 58may execute instruction stored in the memory 56 to perform operations inthe battery system 12, such as instructing a controllable switchingdevice 30 to open or close. As such, the one or more processors 58 mayinclude one or more general purpose microprocessors, one or moreapplication specific processors (ASICs), one or more field programmablelogic arrays (FPGAs), or any combination thereof. Additionally, thememory 56 may include one or more tangible, non-transitory,computer-readable mediums that store instructions executable by and datato be processed by a processor 58. Thus, in some embodiments, the memory56 may include random access memory (RAM), read only memory (ROM),rewritable non-volatile memory such as flash memory, hard drives,optical discs, and the like.

As described above, the battery system 12 may be electrically connectedto electrical components of the vehicle 10. However, architecture (e.g.,configuration of electrical connections) of the battery system 12 mayvary between different implementations. Various architectures may enablethe battery system 12 to divide operations between the first battery 26and the second battery 28. However, control scheme implemented by thecontrol unit 32 may vary based at least in part on architecture of thebattery system 12.

For example, in some embodiments, the first battery 26 and the secondbattery 28 may be connected in various parallel architectures, such as aswitch-passive parallel architecture or an active parallel architecture.In a switch-passive parallel architecture, the battery system 12 mayinclude multiple batteries may be connected in parallel with one or morebeing selectively connected and disconnected by a mechanical switch 52.Additionally, in an active parallel architecture, the battery system 12may include multiple batteries connect in parallel with one or morebeing selectively connected and disconnected by a DC/DC converter 54.

To help illustrate, one embodiment of a switch-passive parallelarchitecture 60 is described in FIG. 8. To simplify discussion, thefirst battery 26 will be described as a lead-acid (PbA) battery 62 andthe second battery 28 will be described as a lithium-ion (Li-ion)battery 64. However, one of ordinary skill in the art should be able toadapt the switch-passive parallel architecture 60 to other pairs ofbattery chemistries.

In the depicted embodiment, the lead-acid battery 62 and the lithium-ionbattery 64 are coupled in parallel with the starter 16, the regenerativebraking system 20, and an electrical system 66 via a bus 25. Asdescribed above, the electrical system 66 is intended to describe otherelectrical components in the vehicle 10, such as the HVAC system 24and/or the vehicle console 22. As depicted, a first mechanical switch52A is electrically coupled between the lead-acid battery 62 and the bus25. Additionally a second mechanical switch 52B is electrically coupledbetween the lithium-ion battery 64 and the bus 25. As such, the controlunit 32 may instruct the first mechanical switch 52A to selectivelyconnect and disconnect the lead-acid battery 62 and the secondmechanical switch 52B to selectively connect and disconnect thelithium-ion battery 64.

In some embodiments, the control unit 32 may instruct the firstmechanical switch 52A and the second mechanical switch 52B toselectively connect and disconnect the lead-acid battery 62 and thelithium ion battery 64 respectively to facilitate dividing operationsbetween the lead-acid battery 62 and the lithium ion battery 64. Forexample, the control unit 32 may instruct the first mechanical switch52A to close and the second mechanical switch 52B to open when coldcranking the internal combustion engine 18. In this manner, thelead-acid battery 62 may be used to cold crank the internal combustionengine 18 by itself. As described above, the lead-acid battery 62 may bebetter suited to cold crank the internal combustion engine 18 due to itsability to operate at lower temperatures and being less affected by deepdischarging.

Additionally, the control unit 32 may instruct the first mechanicalswitch 52A to open and the second mechanical switch 52B to close duringbraking. In this manner, the lithium-ion battery 64 may be used tocapture and store electrical energy generated by the regenerativebraking system 20 by itself. As described above, the lithium-ion battery64 may be better suited to capture electrical energy generated duringregenerative braking due to its higher coulombic efficiency and/orhigher charge power acceptance. In this manner, the switch-passiveparallel battery architecture 60 may enable the control unit 32 todivide operations performed by the battery system 12 between thelead-acid battery 62 and lithium-ion battery 64 based on theirrespective strengths, which may facilitate improving operationalefficiency of the battery system.

In addition to the parallel architectures, the first battery 26 and thesecond battery 28 may be connected in other architectures thatfacilitate dividing operations performed by the battery system 12between the first battery 26 and the second battery 28. For example, insome embodiments, the first battery 26 and the second battery 28 may beconnected in various partial parallel architectures, such as asemi-active partial parallel architecture. As used herein, a “partialparallel architecture” is intended to describe an architecture in whichthe first battery 26 and the second battery 28 and each coupled inparallel with electrical components, but not one another.

To help illustrate, one embodiment of a semi-active partial parallelarchitecture 70 is depicted in FIG. 9. To simplify discussion, the firstbattery 26 will be described as a lead-acid (PbA) battery 62 and thesecond battery 28 will be described as a lithium-ion (Li-ion) battery64. However, one of ordinary skill in the art should be able to adaptthe semi-active partial parallel architecture 70 to other pairs ofbattery chemistries.

As depicted, the lead-acid battery 62 is coupled in parallel with thestarter 16 via a first bus 25A. Additionally, the lithium-ion battery 64is coupled in parallel with the regenerative braking system 20 and theelectrical system 66 via a second bus 25B. Furthermore, a DC/DCconverter 54 and, in some embodiments, a bypass mechanical switch 52Care electrically coupled between the first bus 25A and the second bus25B.

Generally, the DC/DC converter 54 may function similarly to a mechanicalswitch 52 by turning on and off to selectively connect and disconnect.In some embodiments, a DC/DC converter 54 may turn off and, thus,disconnect by outputting zero current. For example, the DC/DC converter54 may maintain an internal switch in a closed position when in a boostconfiguration or maintain an internal switch in an open position when ina buck configuration. Additionally, a DC/DC converter 54 may turn onand, thus, connect by outputting current with a stepped up or steppeddown voltage. For example, the DC/DC converter 54 may maintain theinternal switch when in a boost configuration or a buck configuration.In this manner, the control unit 32 uses the DC/DC converter 54 toselectively connect and disconnect the first bus 25A and the second bus25B and, thus, the lead-acid battery 62 and the lithium-ion battery 64.

As such, the control unit 32 may use the DC/DC converter 54 tofacilitate dividing operations between the lead-acid battery 62 and thelithium ion battery 64. For example, the control unit 32 may instructthe DC/DC converter 54 to disconnect the first bus 25A and the secondbus 25B when cold cranking the internal combustion engine 18. In thismanner, the lead-acid battery 62 may be used to cold crank the internalcombustion engine 18 by itself. Additionally, the control unit 32 mayinstruct the DC/DC converter 54 to disconnect the first bus 25A and thesecond bus 25B when the vehicle 10 is braking. In this manner, thelithium-ion battery 64 may be used to capture and store electricalenergy generated during regenerative braking by itself.

Furthermore, the control unit 32 may instruct the DC/DC converter 54 toconnect the first bus 25A and the second bus 25B during normal operation(e.g., when the vehicle is in motion and not braking). In this manner,the lithium-ion battery 64 may supply electrical power to charge thelead-acid battery in addition to powering the electrical system 66.Thus, similar to the switch-passive parallel battery architecture 60,the semi-active partial parallel architecture 70 may enable the controlunit 32 to divide operations performed by the battery system 12 betweenthe lead-acid battery 62 and lithium-ion battery 64 based at least inpart on their respective strengths.

Although multiple architectures may be suitable to divide operationperformed by the battery system between the first battery 26 and thesecond battery 28, some may present tradeoffs. For example, mechanicalswitches 52 are generally smaller, less costly, and more robust (e.g.,capable of conducting more current) compared to a DC/DC converter 54. Assuch, the switch-passive parallel architecture 60 may be smaller, lesscostly, and more robust compared to the semi-active partial parallelarchitecture 70.

On the other hand, a DC/DC converter 54 may provide greater amounts ofcontrol over operation of the battery system 12 compared to a mechanicalswitch 52. For example, the DC/DC converter 54 may control magnitude ofoutput current. Thus, in some embodiments, the DC/DC converter maycontrol current flowing from the second battery 28 to the first battery26 and, thus, charging rate of the first battery 26. In fact, in someembodiments, the current may be controlled based at least in part oncharge acceptance rate limit of the first battery 26 to improve chargingefficiency (e.g., amount of electrical energy expended compared toamount of electrical energy captured). As such, the semi-active partialparallel architecture 70 may enable the control unit 32 to implementcontrol schemes that further improve operational efficiency compared tothe switch-passive parallel architecture 60.

One embodiment of a process 72 for controlling operation of the batterysystem 12 when a vehicle 10 is transitioned from key off to key on isdescribed in FIG. 10. Generally process 72 includes determining when avehicle transitions to key on (process block 74), supplying electricalpower from a first battery to a starter to cold crank an internalcombustion engine (process block 76), determining whether state ofcharge of a second battery is greater than a threshold (decision block78), and supplying electrical power to the electrical system from analternator and/or the second battery when the state of charge of thesecond battery is not greater than the threshold (process block 80).Additionally, when the state of charge of the second battery is greaterthan the threshold, the process 72 includes supplying electrical powerto the electrical system from the second battery (process block 82),supplying electrical power from the second battery to charge the firstbattery (process block 84), determining whether the vehicle is braking(decision block 86), and supplying electrical power from a regenerativebraking system to the second battery when the vehicle is braking(process block 88). In some embodiments, the process 72 may beimplemented by executing instructions stored in a tangible,non-transitory, computer-readable medium, such as memory 56, usingprocessing circuitry, such as the processor 58.

Accordingly, in some embodiments, the control unit 32 may determine whena vehicle 10 transitions from key off to key on (process block 74). Insome embodiments, the control unit 32 may remain powered on even whenthe vehicle is key off to control supply of electrical power to key offloads, such as the alarm system. In such embodiments, the control unit32 may determine when the transition occurs based on an indication, forexample, from a central control unit or directly from an ignition. Inother embodiment, the control unit 32 may be powered off when thevehicle is key off. In such embodiments, the control unit 32 maydetermine when the transition occurs based on when electrical power issupplied to turn on the control unit 32.

The control unit 32 may then instruct the battery system 12 to supplyelectrical power from the first battery 26 to the starter 16 to coldcrank the internal combustion engine 18 (process block 76). When keyoff, temperature of the battery system 12 may gradually adjust totemperature of its surrounding environment, which is generally lowerthan temperature when the vehicle 10 is key on. In other words, to coldcrank the internal combustion engine 18, a battery may be asked tosupply electrical power while at a lower temperature compared to otherkey on loads. Additionally, cranking the internal combustion engine 18may consume a significant amount of electrical energy. In other words,to crank the internal combustion engine 18, a battery may be drasticallydischarged.

As described above, battery chemistries may be may exhibit differentoperational characteristics. For example, lithium-ion batteries 64 maybe designed to operate in a smaller and/or higher operating temperaturerange and in a smaller and/or higher state of charge range. On the otherhand, lead-acid batteries 62 may be desired to operate in a largerand/or lower operating temperature range and in a larger and/or lowerstate of charge range. In other words, a lead-acid battery 62 may bemore capable of operating at lower operating temperatures and lessaffected by deep discharging. As such, the first battery 26 may be alead-acid battery 62.

In some embodiments, the control unit 32 may instruct the first battery26 to cold crank the internal combustion engine 18 by instructing thebattery system 12 to disconnect the second battery 28 from the starter16. For example, with regard to the semi-active partial parallelarchitecture 70 described in FIG. 9, the control unit 32 may instructthe DC/DC converter 54 to turn off, thereby disconnecting thelithium-ion battery 64 from the starter 16 and enabling the lead-acidbattery 62 to supply electrical power to the starter 16 by itself Inthis manner, operational efficiency of the battery system 12 may beimproved since the lead-acid battery 62 is better suited to cold crankthe internal combustion engine 18.

Returning to the process 72 described in FIG. 10, the control unit 32may then determine whether the state of charge of the second battery 28is greater than an operating range threshold (decision block 78). Insome embodiments, the control unit 32 may determine state of charge ofthe second battery 28 using a state of charge sensor 29. Additionally oralternatively, the control unit 32 may determine state of charge of thesecond battery 28 based on operational parameters of the second battery28, such as open circuit voltage.

The control unit 32 may then determine the operating range threshold andcompare it with the state of charge of the second battery 28. In someembodiments, the operating range threshold may be predetermined, forexample, by a manufacturer, and stored in memory 56. Thus, in suchembodiments, the control unit 32 may retrieve the operating rangethreshold from memory 56. Additionally, in some embodiments, theoperating range threshold may be set so that the second battery 28 ismaintained within a desired state of charge range (e.g., not deepdischarged). Furthermore, in some embodiments, the operating rangethreshold may be set so that the second battery 28 is sufficient topower the electrical system 66 when above the operating range threshold.

Thus, when the state of charge of the second battery 28 is not greaterthan the operating range threshold, the control unit 32 may instruct thebattery system 12 to supply electrical power to the electrical system 66from the second battery 28 and/or the alternator (process block 80).More specifically, the alternator may convert mechanical energy outputby the internal combustion engine 18 into electrical energy. Thus, insome embodiments, the control unit 32 may instruct the battery system 12to disconnect the second battery 28 and supply electrical power to theelectrical system 66 using only the alternator.

In other embodiments, the control unit 32 may instruct the batterysystem 12 to charge the second battery 28 using electrical power outputfrom the alternator. In such embodiments, this may result inmicro-cycling the second battery 28. For example, the control unit 32may instruct the alternator to enable and charge the second battery 28above the operating range threshold. Once above the operating rangethreshold (e.g., by a set amount), the control unit 32 may instruct thealternator to disable and the second battery 28 to supply electricalpower to the electrical system 66. If the second battery 28 againreaches the operating range threshold, the control unit 32 may instructthe alternator to enable and again charge the second battery. Thus, insuch embodiments, the control unit 32 may periodically check whether thestate of charge of the second battery 28 is above the operating rangethreshold (arrow 92).

On the other hand, when the state of charge of the second battery 28 isgreater that the operating range threshold, the control unit 32 mayinstruct the battery system 12 to supply electrical power to theelectrical system 66 from the second battery 28 (process block 82). Asdescribed above, the operating range threshold may be set so that thesecond battery 28 is sufficient to power the electrical system 66 whenabove the operating range threshold. Thus, in some embodiments, whenabove the operating range threshold, the control unit 32 may instructthe battery system 12 to supply electrical power only from the secondbattery 28. In such embodiments, the alternator may be disabled, therebyreducing load on the internal combustion engine 18 and, thus, improvingfuel economy.

Additionally, when the state of charge of the second battery 28 isgreater than the operating range threshold, the control unit 32 mayinstruct the battery system 12 to supply electrical power from thesecond battery 28 to charge the first battery 26 (process block 84). Insome embodiments, the battery system 12 may charge the first battery 26by enabling current for flow from the second battery 28 to the firstbattery 26. For example, with regard to the semi-active partial parallelarchitecture 70 described in FIG. 9, the control unit 32 may instructthe DC/DC converter 54 to produce a current flow from the lithium-ionbattery 64 to the lead-acid battery 62.

As described above, in some embodiments, the DC/DC converter 54 may beboost converter, a buck converter, or a bi-directional converter. Thus,in such embodiments, the DC/DC converter 54 may adjust voltage ofelectrical power output by the lithium-ion battery 64. Thus, the controlunit 32 may instruct the DC/DC converter 54 to output a voltage greaterthan the open-circuit voltage of the lead-acid battery 62. In thismanner, the DC/DC converter 54 may enable current to flow from thelithium-ion battery 64, through the second bus 25B, through the firstbus 25A, and into the lead-acid battery 62. However, due to the highervoltage, the DC/DC converter 54 may block current from flowing from thefirst bus 25A to the second bus 25B.

In addition to merely enabling current to flow, the control unit 32 mayuse the DC/DC converter 54 to control magnitude of the current and,thus, charging rate of the lead-acid battery 62. Specifically, the DC/DCconverter 54 may adjust the current output to the lead-acid battery 62by adjusting its output voltage. For example, as output voltageincreases, the output current may decrease and vice versa.

In some embodiments, the control unit 32 may control current supplied tothe lead-acid battery 62 based at least in part on the charge acceptancerate limit of the lead-acid battery 62. A charge acceptance rate limitmay indicate a limit on amount of electrical energy a battery cancapture and store at one time. Thus, additional electrical energy abovethe charge acceptance rate limit may not be captured and stored in thebattery and, in fact, may cause an undesired temperature increase,polarization, and/or an overcharge condition. As such, the DC/DCconverter 54 may control the current supplied to improve chargingefficiency (e.g., amount of charge used charge) of the lead-acid battery62 and/or to reduce possibility of undesired effects. In fact, since thecharge acceptance rate limit may be low, the DC/DC converter 54 mayrestrict the lead-acid battery 62 to trickle (e.g., gradual) charging,for example, at less than a maximum charging rate.

Additionally, in some embodiments, the control unit 32 may dynamicallycontrol current supplied to the lead-acid battery 62 based at least inpart on power consumption by the electrical system 66. Morespecifically, the lithium-ion battery 64 may output a finite amount ofcurrent at one time. As such, the current may be split betweenconsumption by the electrical system 66 and charging of the lead-acidbattery 62. Accordingly, when consumption by the electrical system 66increases, the control unit 32 may instruct the DC/DC converter 54 todivert more electrical power to the electrical system 66 at the expenseof charging the lead-acid battery 62. On the other hand, whenconsumption by the electrical system 66 decreases, the control unit 32may instruct the DC/DC converter 54 to divert electrical power back tocharging the lead-acid battery 62. In this manner, the DC/DC converter54 may enable the lead-acid battery 62 to be charged withoutsubstantially affecting operation of the electrical system 66.

Returning to the process 72 described in FIG. 10, the control unit 32may also periodically determine whether the vehicle 10 is braking(decision block 86). In some embodiments, the control unit 32 mayreceive an indication of whether the vehicle 10 is braking, for example,from a central control unit and/or the brakes. In other embodiments, thecontrol unit 32 may determine whether the vehicle 10 is braking based onoperational characteristics of the vehicle, such as speed of the vehicle10 and/or revelations per minute (RPM) of the internal combustion engine18. For example, the control unit 32 may determine that the vehicle 10is braking when speed of the vehicle drastically decreases.

When the vehicle 10 is not braking, the control unit 32 may return todetermining whether state of charge of the second battery 28 is lessthan the operating range threshold (arrow 90). On the other hand, whenthe vehicle 10 is braking, the control unit 32 may instruct theregenerative braking system 20 to supply electrical power to the secondbattery 28 (process block 88). As described above, the regenerativebraking system 20 may converter mechanical (e.g., kinetic) energy of thevehicle 10 into electrical energy, which may be output as electricalpower. Thus, supplying the electrical power to the second battery 28 mayenable the second battery 28 to capture and store electrical energygenerated during regenerative braking for subsequent use in the vehicle10.

As described above, capturing electrical energy generated duringregenerative braking may enable disabling the alternator for periods oftime, which facilitates improving fuel economy of the vehicle 10. Thus,such benefits may be improved by increasing amount of electrical energythat is actually captured and stored by the battery system 12.Generally, braking is intended to quickly reduce speed and, thus,mechanical energy of the vehicle 10 over a short time. As such, theelectrical power output from the regenerative braking system 20 may behigh and last a short period of time. In other words, the battery system12 may improve benefits of the regenerative braking system 20 by using abattery chemistry for the second battery 28 that increases amount ofelectrical energy it is able to capture at one time.

As described above, some battery chemistries may be may exhibitdifferent operational characteristics. For example, lead-acid batterychemistries may have a lower coulombic efficiency and/or lower chargeacceptance rate limit, which may limit amount of electrical energycaptured at one time. On the other hand, lithium-ion battery chemistriesmay have a higher coulombic efficiency and/or a higher charge acceptancerate limit. In other words, lithium ion battery chemistries may be morecapable of capturing a large amount of electrical energy over a shortperiod of time. As such, the second battery 28 may be a lithium-ionbattery 64.

In some embodiments, the control unit 32 may instruct the second battery28 to capture and store the electrical energy generated by theregenerative braking system 20 by instructing the battery system 12 todisconnect the first battery 26 from the regenerative braking system 20.For example, with regard to the semi-active partial parallelarchitecture 70 described in FIG. 9, the control unit 32 may instructthe DC/DC converter 54 to turn off, thereby disconnecting the lead-acidbattery 62 from the regenerative braking system 20 and enabling thelithium-ion battery 64 to capture electrical energy generated duringregenerative braking by itself. In this manner, operational efficiencyof the battery system 12 may be improved since the lithium-ion battery64 is better suited to capture electrical energy generated duringregenerative braking.

As described above, in some embodiments, the vehicle 10 may be amicro-hybrid vehicle. In such embodiments, the vehicle 10 may disablethe internal combustion engine 18 when the vehicle is idle (e.g.,stopped) and key on. Subsequently, the battery system 12 may supplyelectrical power to the starter 16 to warm crank the internal combustionengine 18 when propulsion is desired.

Since a vehicle 10 is generally transitioned to the key off whenexpected to be idle for extended periods of time, it can be assumed thatthe internal combustion engine 18 has been in operation relativelyrecently (e.g., second or minutes) when warm cranked. Accordingly,temperature of the battery system 12 and, specifically, the secondbattery 28 is generally when the internal combustion engine 18 is warmcranked compared to when the internal combustion engine 18 is coldcranked. Thus, in some embodiments, the second battery 28 may be used inaddition to or in alternative to the first battery 26 when warm crankingthe internal combustion engine 18.

In other words, in some embodiments, the battery system 12 may use thefirst battery 26, the second battery 28, or both to warm crank theinternal combustion engine 18. In fact, in some embodiments, the controlunit 32 may dynamically adjust combination of the first battery 26 andthe second battery 28 used to warm crank the internal combustion engine18 based at least in part on operational parameters of the secondbattery 28 and/or the first battery 26. For example, the control unit 32may determine whether to use the second battery 28 based at least inpart on temperature of the second battery 28. Specifically, the controlunit 32 may instruct the second battery 28 to supply electrical power towarm crank when temperature of the second battery 28 is within a desiredoperating range. Additionally or alternatively, the control unit 32 maydetermine whether to use the second battery 28 based at least in part onstate of charge of the first battery 26 and/or the state of charge ofthe second battery 28.

To help illustrate, one embodiment of a process 96 for dynamicallyadjusting batteries used to warm crank an internal combustion engine 18is described in FIG. 11. Generally, the process 96 includes determiningthat a vehicle is key on and idle (process block 98), disabling aninternal combustion engine (process block 100), and determining whetherpropulsion is desired (decision block 102). Additionally, whenpropulsion is desired, the process 96 includes determining state of thecharge of a first battery and a second battery (process block 104),determining whether state of charge of the second battery is greaterthan a first threshold (decision block 106), and determining whetherstate of charge of the first battery is greater than a second threshold(decision block 108). Additionally, the process 96 includes supplyingelectrical power from the second battery to the starter to warm crankthe internal combustion engine when state of the charge of the firstbattery is not less than the second threshold (process block 110) andsupplying electrical power from the first battery and the second batteryto the starter to warm crank the internal combustion engine when thestate of charge of the second battery is greater than the firstthreshold or the state of charge of the second battery is less than thesecond threshold (process block 112). In some embodiments, the process96 may be implemented by executing instructions stored in a tangible,non-transitory, computer-readable medium, such as memory 56, usingprocessing circuitry, such as the processor 58.

Accordingly, in some embodiments, the control unit 32 may the controlunit 32 may determine the vehicle 10 is key on and idle (process block98). In some embodiments, the control unit 32 may receive an indicationof whether the vehicle 10 is key on and idle, for example, from acentral control unit and/or the speedometer. In other embodiments, thecontrol unit 32 may determine whether the vehicle 10 is key on and idlebased on operational characteristics of the vehicle, such as speed ofthe vehicle 10 and/or revelations per minute (RPM) of the internalcombustion engine 18. For example, the control unit 32 may determinethat the vehicle 10 is key on and idle when speed of the vehicle 10 iszero while RPM of the internal combustion engine 18 is non-zero.

When the vehicle 10 is key on and idle, the control unit 32 may instructthe internal combustion engine 18 to disable (process block 98).Disabling the internal combustion engine 18 may reduce fuel consumptionand, thus, improve fuel economy of the vehicle 10. While the internalcombustion engine 18 is disabled, the second battery 28 may continuesupplying electrical power to the electrical system 66.

Additionally, the control unit 32 may periodically determine whetherpropulsion is desired. In some embodiments, the control unit 32 mayreceive an indication of whether the propulsion is desired, for example,from a central control unit. In such embodiments, the control unit 32may receive an indication that propulsion is desired when gas pedal ofthe vehicle 10 is depressed, brake pedal of the vehicle 10 is released,and/or the vehicle 10 is shifted into drive.

As described above, the control unit 32 may determine whether to use thefirst battery 26, the second battery 28, or both to warm crank theinternal combustion engine based at least in part on operationalparameters of the first battery 26 and/or the second battery 28. Thus,in some embodiments, the control unit 32 may determine state of chargeof the first battery 26 and state of charge of the second battery 28(process block 104). In some embodiments, the control unit 32 maydetermine state of charge of the first battery 26 and/or the secondbattery 28 using one or more state of charge sensors. Additionally oralternatively, the control unit 32 may determine state of charge of thefirst battery 26 and/or the second battery 28 based on respectiveoperational parameters, such as open circuit voltage.

The control unit 32 may then determine whether state of charge of thesecond battery 28 is greater than a first warm crank threshold (decisionblock 106). In some embodiments, the first warm crank threshold may bepredetermined, for example, by a manufacturer and stored in memory 56.Thus, in such embodiments, the control unit 32 may retrieve the firstwarm crank threshold from memory 56. Additionally, in some embodiments,the first warm crank threshold may be set such that state of charge ofthe second battery 28 is expected to remain above the operating rangethreshold even if the second battery 28 is used to warm crank theinternal combustion engine 18 by itself

Thus, in some embodiments, the control unit 32 may instruct the secondbattery 28 to supply electrical power to the starter 16 by itself towarm crank the internal combustion engine 18 when state of charge of thesecond battery is greater than the first warm crank threshold. Forexample, with regard to the semi-active partial parallel architecture 70described in FIG. 9, the control unit 32 may instruct the DC/DCconverter 54 to output a voltage greater than the open-circuit voltageof the lead-acid battery 62. As such, current may flow from thelithium-ion battery 64, through the second bus 25B, through the firstbus 25A, and into the lead-acid battery 62 and/or the starter 16.However, in such embodiments, the current capacity and, thus, size andcost of the DC/DC converter 54 may be increased to enable sufficientcurrent to flow from the lithium-ion battery 64 to crank the internalcombustion engine 18.

Accordingly, in other embodiments such as the process 96 described inFIG. 11, the control unit 32 may instruct the first battery 26 and thesecond battery 28 to supply electrical power to the starter to warmcrank the internal combustion engine 18 even when state of charge of thesecond battery is greater than the first warm crank threshold (processblock 112). For example, with regard to the semi-active partial parallelarchitecture 70 described in FIG. 9, the control unit 32 may instructthe DC/DC converter 54 to output a voltage less than the open-circuitvoltage of the lead-acid battery 62. In this manner, current may fromthe current may flow from the lithium-ion battery 64, through the secondbus 25B, through the first bus 25A, and into the starter 16.Additionally, the DC/DC converter 54 may block current from flowing fromthe first bus 25A to the second bus 25B so that current may flow fromthe lead-acid battery 62, through the first bus 25A, and into thestarter 16.

Additionally, the control unit 32 may determine whether state of chargeof the first battery 26 is greater than a second warm crank threshold(decision block 108). In some embodiments, the second warm crankthreshold may be predetermined, for example, by a manufacturer andstored in memory 56. Thus, in such embodiments, the control unit 32 mayretrieve the second warm crank threshold from memory 56. Additionally,in some embodiments, the second warm crank threshold may be set suchthat the first battery 26 contains sufficient charge to warm crank theinternal combustion engine 18 by itself when not less than the secondwarm crank threshold.

Thus, when state of charge of the first battery 26 is less than thesecond warm crank threshold, the control unit 32 may instruct the firstbattery 26 and the second battery 28 to supply electrical power to thestarter 16 to warm crank the internal combustion engine 18 (processblock 112). On the other hand, when the state of charge of the firstbattery 26 is not less than the second warm crank threshold, the controlunit 32 may instruct the first battery 26 to supply electrical power tothe starter 16 to warm crank the internal combustion engine (processblock 110).

In some embodiments, similar to cold cranking, the control unit 32 mayinstruct the first battery 26 to warm cranking the internal combustionengine 18 by instructing the battery system 12 to disconnect the secondbattery 28 from the starter 16. For example, with regard to thesemi-active partial parallel architecture 70 described in FIG. 9, thecontrol unit 32 may instruct the DC/DC converter 54 to turn off, therebydisconnecting the lithium-ion battery 64 from the starter 16 andenabling the lead-acid battery 62 to supply electrical power to thestarter 16 by itself.

Based on the above described examples, the battery system 12 may utilizethe first battery 26 to crank (e.g., cold crank and/or warm crank) theinternal combustion engine and the second battery 28 to support theelectrical system 66 when the vehicle 10 is key on. In other words, insuch embodiments, the operations performed by the first battery 26 maybe reduced. As such, in some embodiments, this may facilitate reducingstorage capacity and, thus, physical size of the first battery 26.However, particularly with reduced storage capacity, the first battery26 should still remain sufficiently charged to cold crank the internalcombustion engine 18 when desired. To facilitate, the second battery 28may charge the first battery 26 when the vehicle 10 is key off.

To help illustrate, one embodiment of a process 114 for operating thebattery system 12 when the vehicle 10 is transitioned to key off isdescribed in FIG. 12. Generally, the process 114 includes determiningthat a vehicle transitions to key off (process block 116), determiningstate of charge of a first battery (process block 118), determiningwhether state of charge of the first battery is less than a threshold(decision block 120), and supplying electrical power from a batterysystem to an electrical system when state of charge of the first batteryis not less than the threshold (process block 122). Additionally, whenstate of charge of the first battery is less than the threshold, theprocess 114 includes supplying electrical power from a second battery tothe electrical system (process block 124) and supplying electrical powerfrom the second battery to the first battery (process block 126). Insome embodiments, the process 114 may be implemented by executinginstructions stored in a tangible, non-transitory, computer-readablemedium, such as memory 56, using processing circuitry, such as theprocessor 58.

Accordingly, in some embodiments, the control unit 32 may determine whena vehicle 10 transitions from key on to key off (process block 116). Asdescribed above, in some embodiments, the control unit 32 may remainpowered on even when the vehicle is key off to control distribution ofelectrical power, for example, to key off loads, such as the alarmsystem. In such embodiments, the control unit 32 may determine when thetransition occurs based on an indication, for example, from a centralcontrol unit or directly from the ignition.

Additionally, the control unit 32 may determine state of charge of thefirst battery (process block 118). In some embodiments, the control unit32 may determine state of charge of the first battery 26 using one ormore state of charge sensors 29. Additionally or alternatively, thecontrol unit 32 may determine state of charge of the first battery 26based operational parameters of the first battery 26, such as opencircuit voltage.

The control unit 32 may then determine whether state of charge of thefirst battery 26 is greater than a cold crank threshold (decision block120). In some embodiments, the cold crank threshold may bepredetermined, for example, by a manufacturer, and stored in memory 56.Thus, in such embodiments, the control unit 32 may retrieve the secondwarm crank threshold from memory 56. Additionally, in some embodiments,the cold crank threshold may be set such that the first battery 26contains sufficient charge to cold crank the internal combustion engine18 by itself when not less than the cold crank threshold. Thus, in someembodiments, the cold crank threshold may be the same or relativelysimilar to the second warm crank threshold.

When state of charge of the first battery 26 is less than the cold crankthreshold, the control unit 32 may instruct the battery system 12 tosupply electrical power to the electrical system 66 from the secondbattery 28 (process block 124). In some embodiments, the second battery28 may supply electrical power to the electrical system 66 similar towhen the vehicle is key on. In this manner, the second battery 28 maysupply electrical power to key off loads.

Additionally, when state of charge of the first battery is less than thecold crank threshold, the control unit 32 may instruct the batterysystem 12 to supply electrical power to charge the first battery 26(process block 126). In some embodiments, the second battery 28 maycharge the first battery 26 similar to when the vehicle 10 is key on.For example, with regard to the semi-active partial parallelarchitecture 70 described in FIG. 9, the control unit 32 may instructthe DC/DC converter 54 to produce a current flow from the lithium-ionbattery 64 to the lead-acid battery 62. As described above, in someembodiments, the DC/DC converter 54 may control current flow and, thus,charging rate of the lead-acid battery 62, for example, based at leastin part on charge acceptance rate of the lead-acid battery 62 and/orpower consumption by the electrical system 66.

Returning to the process 114 described in FIG. 12, the control unit 32may periodically check if state of charge of the first battery 26 isless than the cold crank threshold (arrow 128). When state of charge ofthe first battery 26 is not less than the cold crank threshold, thecontrol unit 32 may instruct the battery system 12 to supply electricalpower to the electrical system 66 (process block 122). In this manner,the battery system 12 may supply electrical power to key off loads.

In some embodiments, the second battery 28 may support the key offloads. As such, the second battery 28 may supply electrical power to theelectrical system 66 (process block 130). For example, with regard tothe semi-active partial parallel architecture 70 described in FIG. 9,the control unit 32 may instruct the DC/DC converter 54 to turn off,thereby disconnecting the first bus 25A from the second bus 25B andenabling the lithium-ion battery 64 to support the key off load byitself.

Additionally or alternatively, the first battery 26 may support key offloads. In some embodiments, the first battery 26 may supply electricalpower to the electrical system 66 via a DC/DC converter 54 (processblock 132). For example, with regard to the semi-active partial parallelarchitecture 70 described in FIG. 9, the control unit 32 may instructthe DC/DC converter 54 to adjust voltage output to the electrical system66. As such, the DC/DC converter 54 may facilitate using the lead-acidbattery 62 to support key off loads even when the electrical system 66is designed to use different voltage electrical power than output fromthe lead-acid battery 62. For example, when the electrical system 66 isdesired to operate with forty-eight volt electrical power and thelead-acid battery 62 outputs twelve volt electrical power, the DC/DCconverter 54 may boost the output voltage to forty-eight volts tofacilitate use with the electrical system 66.

In other embodiments, the first battery 26 may supply electrical powerto the electrical system 66 via a bypass mechanical switch 52C (processblock 134). For example, with regard to the semi-active partial parallelarchitecture 70 described in FIG. 9, the control unit 32 may instructthe battery system 12 to close the bypass mechanical switch 52C. Assuch, the bypass mechanical switch 52C may directly connect lead-acidbattery 62 to the electrical system 66, thereby bypassing the DC/DCconverter 54. Since a DC/DC converter 54 is generally more lossy (e.g.,consumes electrical energy) than a mechanical switch 52, closing thebypass switching 52C may facilitate improving electrical powerdistribution efficiency from the lead-acid battery 62 to the key offloads. However, the bypass mechanical switch 52C may provide the controlunit 32 less control over the distribution of electrical power.

Thus, one or more of the disclosed embodiments, alone or on combination,may provide one or more technical effects including improvingoperational efficiency of a battery system in a vehicle context. Forexample, the battery system may include multiple batteries with varyingbattery configurations. In some embodiments, the battery system mayutilize a first battery and a second battery with differing batterychemistries and, thus, different operating strengths. For example, thefirst battery may be a lead-acid battery and the second battery may belithium-ion battery. To utilize the strengths of the different batterychemistries, the battery system may be operated to divide operationsbetween the first battery and the second battery. For example, thelead-acid battery may be dedicated to cold cranking an internalcombustion engine due to its ability to operate at lower temperaturesand being less affected by deep discharging. Additionally, thelithium-ion battery may be dedicated to capturing electrical energygenerated during regenerative braking due to its higher coulombicefficiency and/or charge acceptance rate limit. In this the operationsperformed by the battery system may be divided between the multiplebatteries based at least in part on their strengths, which mayfacilitate improving operational efficiency of the battery system.

The specific embodiments described above have been shown by way ofexample, and it should be understood that these embodiments may besusceptible to various modifications and alternative forms. It should befurther understood that the claims are not intended to be limited to theparticular forms disclosed, but rather to cover all modifications,equivalents, and alternatives falling within the spirit and scope ofthis disclosure.

1. A battery system comprising: a first battery electrically coupled toa first bus, wherein the first battery is configured to output firstelectrical power to the first bus to enable a starter electricallycoupled to the first bus to crank an internal combustion engine; asecond battery electrically coupled to a second bus, wherein the secondbattery is configured to: store electrical energy generated by aregenerative braking system; and output second electrical power to thesecond bus using the electrical energy stored in the second battery toenable the battery system to power operation of an electrical componentcoupled to the second bus; and a DC/DC converter electrically coupledbetween the first bus and the second bus, wherein the DC/DC converter isconfigured to control division of the second electrical power outputfrom the second battery into a first portion supplied to charge thefirst battery via the first bus and a second portion supplied to operatethe electrical component via the second bus.
 2. The battery system ofclaim 1, wherein: the first battery comprises one or more lead-acidbattery cells; and the second battery comprises one or more lithium-ionbattery cells.
 3. The battery system of claim 1, wherein the batterysystem is configured to: supply the first electrical power output fromthe first battery to the starter to crank the internal combustion enginewhen an automotive vehicle transitions from key-off to key-on; andsupply third electrical power to the starter to crank the internalcombustion engine while the automotive vehicle is key-on to transitionthe automotive vehicle out of an idle state, wherein: the first batteryis configured to supply a first portion of the third electrical powerand the second battery is configured to supply a second portion of thethird electrical power when a state of charge of the second battery isgreater than a first threshold or a state of charge of the first batteryis less than a second threshold; and the first battery is configured tosupply the third electrical power by itself when the state of charge ofthe first battery is not less than the second threshold.
 4. The batterysystem of claim 1, wherein, to control division of the second electricalpower, the DC/DC converter is configured to control current flow fromthe second bus to the first bus based at least in part on chargeacceptance rate limit of the first battery, power consumption by theelectrical component, or both.
 5. The battery system of claim 1, whereinthe second battery comprises one or more lithium nickel manganese cobaltoxide battery cells, one or more lithium-titanate/lithium nickelmanganese cobalt oxide battery cells, one or morelithium-titanate/lithium manganese oxide battery cells, one or morelithium iron phosphate battery cells, or any combination thereof
 6. Thebattery system of claim 1, comprising: a first positive terminalconfigured to electrically couple the first battery to the first bus; asecond positive terminal configured to electrically coupled the secondbattery to the second bus; and a negative terminal configured toelectrically couple the first battery and the second battery to ground.7. A battery module comprising: a first battery comprising one or morelead-acid battery cells; a first positive terminal coupled to the firstbattery, wherein the first positive terminal is configured toelectrically couple the first battery to a first bus to enable the firstbattery to output at least a portion of first electrical power used tocrank an internal combustion engine; a second battery comprising one ormore lithium-ion battery cells; a second positive terminal coupled tothe second battery, wherein the second positive terminal is configuredto electrically couple the second battery to a second bus to enable thesecond battery to capture electrical energy generated by a regenerativebraking system and to output second electrical power used to poweroperation of an electrical system; and a negative terminal coupled tothe first battery and the second battery, wherein the negative terminalis configured to electrically couple the first battery and the secondbattery to ground.
 8. The battery module of claim 7, comprising aswitching device electrically coupled between the first battery and thesecond battery, wherein the switching device is configured to controlcurrent flow between the first bus and the second bus.
 9. The batterymodule of claim 8, wherein the switching device comprises a DC/DCconverter configured to control division of the second electrical poweroutput from the second battery into: a first portion of the secondelectrical power supplied to the electrical system via the second bus;and a second portion of the second electrical power supplied to thefirst bus to charge the first battery.
 10. The battery module of claim8, comprising a housing, wherein: the first battery, the second battery,and the switching device are disposed within the housing; and the firstpositive terminal, the second positive terminal, and the negativeterminal extend through the housing.
 11. The battery module of claim 7,wherein the battery module only includes three terminals.
 12. Thebattery module of claim 7, wherein: the one or more lead-acid batterycells are configured to produce a first open circuit voltage within afirst voltage range across the first battery; and the one or morelithium-ion battery cells are configured to produce a second opencircuit voltage within a second voltage range that is greater than thefirst voltage range across the second battery.
 13. The battery module ofclaim 7, wherein: the first battery comprises a twelve volt battery; thefirst positive terminal comprises a positive twelve volt terminal; thesecond battery comprises a forty-eight volt battery; and the secondpositive terminal comprises a positive forty-eight volt terminal. 14.The battery module of claim 7, wherein: the first battery comprise afirst voltage class battery configured to produce a first voltage withina first voltage range; and the second battery comprises a second voltageclass battery configured to produce a second voltage within a secondvoltage range that is greater than the first voltage range.
 15. Thebattery module of claim 7, wherein: the first positive terminal isassociated with a first voltage range; and the second positive terminalis associated with a second voltage range that is greater than andnon-overlapping with the first voltage range.
 16. The battery module ofclaim 7, wherein: the first battery is configured to supply the firstelectrical power used by a starter to crank the internal combustionengine by itself when an automotive vehicle transitions from key-off tokey-on; and to transition the automotive vehicle out of an idle statewhile key-on: the first battery is configured to supply a first portionof the first electrical power and the second battery is configured tosupply a second portion of the first electrical power used by thestarter to crank the internal combustion engine when a state of chargeof the second battery is greater than a first threshold or a state ofcharge of the first battery is less than a second threshold; and thefirst battery is configured to supply the first electrical power used bythe starter to crank the internal combustion engine by itself when thestate of charge of the first battery is not less than the secondthreshold.
 17. An automotive system comprising: a first batterycomprising a first one or more battery cells that each utilizes a firstbattery chemistry; and a control unit programmed to operate the firstbattery as a dedicated starter battery, wherein, to operate the firstbattery as the dedicated starter battery, the control unit is programmedto: determine that actuation of an internal combustion engineimplemented in the automotive system is desired when a first indicationis received from a first user input device; and control operation of theautomotive system such that the first battery completely supplieselectrical power used by a starter implemented in the automotive systemto crank the actuation of the internal combustion engine when desire toactuate the internal combustion engine is determined in response toreceipt of the first indication from the first user input device. 18.The automotive system of claim 17, comprising: a first switching deviceelectrically coupled between the first battery and the starter on afirst bus; a second battery electrically coupled to a second bus,wherein the second bus is configured to electrically couple the secondbattery and one or more electrical components implemented in theautomotive system; and a second switching device electrically coupledbetween the first bus and the second bus, wherein the control unit isprogrammed to: determine that actuation of the internal combustionengine implemented in the automotive system is desired when a secondindication is received from a second user input device; and controloperation of the automotive system such that the first battery suppliesa first portion of the electrical power used by the starter to crank theactuation of the internal combustion engine and the second batterysupplies a second portion of the electrical power used by the starter tocrank the actuation of the internal combustion engine when desire toactuate the internal combustion engine is determined in response toreceipt of the second indication from the second user input device. 19.The automotive system of claim 18, wherein the second switching devicecomprises a DC/DC converter.
 20. The automotive system of claim 18,wherein, to control operation of the automotive system, the control unitis programmed to: when desire to actuate the internal combustion engineis determined in response to receipt of the first indication from thefirst user input device, instruct the switching device to maintain thefirst bus and the second bus electrically disconnected while the firstbattery supplies the electrical power to the starter to cold crank theinternal combustion engine; and when desire to actuate the internalcombustion engine is determined in response to receipt of the secondindication from the second user input device: determine a first state ofcharge of the first battery and a second state of charge of the secondbattery; instruct the switching device to electrically connect the firstbus and the second bus when the second state of charge of the secondbattery is greater than a first threshold or the first state of chargeof the first battery is less than a second threshold to enable the firstbattery to supply the first portion and the second battery to supply thesecond portion of the electrical power used by the starter to warm crankthe actuation of the internal combustion; and instruct the switchingdevice to maintain the first bus and the second bus electricallydisconnected while the first battery supplies the electrical power tothe starter to warm crank the internal combustion engine when the firststate of charge of the first battery is not less than the secondthreshold.
 21. The automotive system of claim 18, wherein: the firstuser input device comprises an ignition switch configured to output thefirst indication that the actuation of the internal combustion engine isdesired when transitioned from a key-off position to a key-on position;and the second user input device comprises: a gas pedal configured tooutput the second indication that the actuation of the internalcombustion engine is desired when depressed; a brake pedal configured tooutput the second indication that the actuation of the internalcombustion engine is desired when released; or a shifter configured tooutput the second indication that the actuation of the internalcombustion engine is desired when shifted into drive.
 22. The automotivesystem of claim 17, wherein the first battery comprises a dedicatedlead-acid starter battery or a dedicated lithium-ion starter battery.23. The automotive system of claim 17, wherein the first batterycomprises a twelve volt starter battery or a forty-eight volt starterbattery.